Background: While the atypical antipsychotics should ultimately reduce the prevalence of tardive dyskinesia, it is likely to remain a significant clinical problem for a long time to come. No strategy has clearly emerged as the treatment of choice for tardive dyskinesia. Atypical antipsychotics have reduced propensities for producing acute extrapyramidal symptoms (EPS) and possibly tardive dyskinesia and may be effective in treating patients with established tardive dyskinesia.

Method: This 12-month, randomized, investigator-blinded study compared the efficacy of quetiapine (N = 22) and haloperidol (N = 23) in treating patients with DSM-IV schizophrenia or schizoaffective disorder and established tardive dyskinesia. Dyskinesia was assessed using the Extrapyramidal Symptom Rating Scale (ESRS) dyskinesia subscale scores and the Clinical Global Impression (CGI) dyskinesia scores. Other EPS, weight, serum prolactin level, and glycosylated hemoglobin level were also assessed. Subjects were enrolled in the study between April 2000 and March 2002.